The present invention relates to a method and an apparatus for mixing a high-viscosity material into a gas and a piston pump used therefor. For example, the present invention is applied to a process prior to foaming for producing a foamed-in-place gasket or a fill foam in a void.
The present invention also relates to a method and an apparatus for foaming a high-viscosity material and is applied to, for example, a foamed-in-place gasket, filling of a void, etc.
FIG. 5 is a fluid circuit diagram of a foaming apparatus 90 using a conventional mixing device.
In FIG. 5, a high-viscosity material contained. in a container 91 is pressurized by a pump 92 and is transferred to a power mixer 94. A compressed gas in a gas cylinder 93 is adjusted to have a high pressure and is transferred to the power mixer 94.
The power mixer 94 is operated by rotating a motor M. The power mixer 94 mixes, under high pressure, a combination of the high-viscosity material and the gas supplied thereto to make the mixture thereof. The mixture of the high-viscosity material and the gas mixed by the power mixer 94 is discharged from a nozzle 96 through a pipe 95. As the gas, a nitrogen gas, a carbonic acid gas or air can be used. The foaming apparatus 90 arranged as mentioned above is used for, for example, applying a high-viscosity polymeric material such as a hotmelt adhesive (see Unexamined Japanese Patent Application Public Disclosure No. 63-264327).
A hotmelt adhesive comprises a thermoplastic polymer which is in a solid form at room temperature. The hotmelt adhesive is melted and fluidized by heating. When the hotmelt adhesive in a molten state is cooled to room temperature, the adhesive solidifies and exerts not only adhesive strength, but also exerts physical strength as a solid mass. In conventional foaming apparatuses for a hotmelt adhesive, a mixture of a gas and a molten hotmelt adhesive is cooled before occurrence of an escape of the gas and then, the mixture is foamed, with the gas being incorporated into the hotmelt adhesive by utilizing the strength of the adhesive which is exerted immediately after cooling.
In the above-mentioned conventional foaming apparatus 90, in order to mix the high-viscosity material and the gas, the high-viscosity material and the gas after heating must be transferred under high pressure to the power mixer 94. When the viscosity of the high-viscosity material is as high as, for example, 100,000 cps, it is considered that the internal pressure of the power mixer 94 is 100 kg/cm2 or more. Therefore, in order to supply the gas and the high-viscosity material to the power mixer 94 at the same time, the pressure of the gas needs to be higher than that of the high-viscosity material.
In the conventional foaming apparatus 90, the amount of gas is measured by controlling the flow rate of the gas. However, when the pressure of the gas is high, it is difficult to control the gas flow rate. Further, a minor error in the gas flow rate under high pressure becomes a major error under atmospheric pressure. For example, an error in the flow rate of 50 kg/cm2 becomes 50 times greater under atmospheric pressure. Therefore, in the conventional foaming apparatus 90, there are great variations in the mixing ratio of the high-viscosity material and the gas, so that foaming ratio cannot be stably conducted, thus making it difficult to achieve uniform foaming ratio.
Further, the high-pressure gas cylinder 93 for supplying the gas must be replaced when the compressed gas in the high-pressure gas cylinder 93 has been exhausted, so that maintenance becomes cumbersome. Further, for replacement of the high-pressure gas cylinder 93, another high-pressure gas cylinder 93 must be installed as a spare, so that a large space is required for installment of these gas cylinders. In addition, various measures must be taken from the viewpoint of safety, according to regulations for high-pressure gases. For these reasons, the conventional foaming apparatus is disadvantageous in terms of costs. SUMMARY OF THE INVENTION
In view of the above, the present invention has been made. It is an object of the present invention to provide a method and an apparatus for mixing a high-viscosity material into a gas and a piston pump used therefor, which enable the gas to be mixed or introduced into the high-viscosity material under low pressure and which achieves an accurate mixing ratio of the gas and the high-viscosity material.
It is another object of the present invention to provide a method and an apparatus four foaming a high-viscosity material, which enable the gas to be introduced into the high-viscosity material under low pressure and which are free from the problems accompanying the conventional technique due to the use of a high-pressure gas cylinder anal ensure easy maintenance, high safety and low costs.
In the method of the present invention, by using a piston pump comprising a piston and a cylinder, the piston being adapted to reciprocally move within the cylinder to effect a suction stroke and a discharge stroke, a gas and a high-viscosity material are supplied separately from each other into the cylinder in a batchwise manner so as to supply the gas during and/or after the suction stroke of the piston pump and to supply the high-viscosity material in the cylinder after the suction stroke. The discharge stroke of the piston pump is effected after completion of the supply of the high-viscosity material in the cylinder, to thereby discharge the gas and the high-viscosity material into a pipe.
In the method of the present invention, a dead space within the cylinder may become substantially zero at the condition of completion of the discharge stroke of the piston pump.
The apparatus of the present invention comprises a piston pump including a piston and a cylinder. The piston is adapted to reciprocally move within the cylinder to effect a suction stroke and a discharge stroke: A gas supplying device supplies a gas into the cylinder under a predetermined pressure and a high-viscosity material supplying device supplies a high-viscosity material into the cylinder under a predetermined pressure. A control device effects control to supply the gas and the high-viscosity material separately from each other into the cylinder in a batchwise manner so that the gas is supplied during and/or after the suction stroke of the piston pump and the high-viscosity material is supplied after the suction stroke, and to effect the discharge stroke of the piston pump after completion of the supply of the high-viscosity material in the cylinder to discharge the gas and the high-viscosity material into a pipe.
In the apparatus of the present invention, first, second and third needle valves may be provided in the cylinder of the piston pump. The first needle valve is provided at a stroke end of the discharge stroke and adapted to control discharge, the second needle valve is provided in the vicinity of the stroke end of the and discharge and discharge stroke and adapted to control supply of the gas, and the third needle valve is provided in the vicinity of a stroke end of the suction stroke and adapted to control supply of the high-viscosity material. A dead space within the cylinder may become substantially zero at the condition of completion of the discharge stroke of the piston pump.
The piston pump of the present invention comprises a cylinder and a piston which reciprocally moves within the cylinder to effect a suction stroke and a discharge stroke. First, second and third needle valves are provided in the cylinder of the piston pump, the first needle valve being provided at a stroke end of the discharge stroke and adapted to control discharge, the second needle valve being provided in the vicinity of the stroke end of the discharge stroke and adapted to control supply of the gas, and third needle valve being provided in the vicinity of a stroke end of the suction stroke and adapted to control supply of the high-viscosity material. A dead space within the cylinder becomes substantially zero at the condition of completion of the discharge stroke of the piston pump.
The method of the present invention comprises: a first step of introducing a high-viscosity material into a gas; a second step of pressurizing, by means of a pump, a combination of the high-viscosity material and the gas transferred from the first step; a third step of passing the combination in a pressurized state through a dispersing pipe to thereby disperse the gas into the high-viscosity material to produce a mixture; and a fourth step of discharging the mixture which a has been passed through the dispersing pipe, to thereby effect foaming. In the first step, use is made of a piston pump including a cylinder and a piston which reciprocally moves within the cylinder to effect a suction stroke and a discharge stroke and a membrane gas generator to which compressed air is supplied to generate a gas. A low-pressure gas generated by the membrane gas generator is supplied into the piston pump to introduce the high-viscosity material into the gas, for example, in a batchwise manner. It should be noted that introducing the high-viscosity material into the gas in a batchwise manner is conducted by supplying the gas into the piston pump separately from the high-viscosity material.
In the method of the present invention, a nitrogen gas may be generated by the membrane gas generator and the generated nitrogen gas may be used as the gas. Dry air may be generated by passing air through a drier and the dry air may be used as the gas.
The method of the present invention may further include the steps of: supplying the gas into the cylinder during and/or after the suction stroke of the piston pump; supplying the high-viscosity material into the cylinder after the suction stroke; and effecting the discharge stroke of the piston pump after completion of the supply of the high viscosity material in the cylinder, to thereby discharge the gas and the high-viscosity material into a pipe.
In the method of the present invention, a mixing ratio of the gas and the high-viscosity material may be controlled based on a supply pressure ratio of the gas to the high viscosity material supplied into the cylinder of the piston pump.
In the method of the present invention, a mixing ratio of the gas and the high-viscosity material may be controlled, by means of a gas pressure, an volume of the gas supplied into the cylinder of the piston pump.
The apparatus of the present invention comprises a membrane gas generator to which compressed air is supplied to generate a nitrogen gas. A high-viscosity pump pumps a high-viscosity material. A piston pump including a piston and a cylinder, the piston being adapted to reciprocally move within the cylinder to effect a suction stroke and a discharge stroke. The piston pump is adapted to discharge a combination of the high-viscosity material pumped from the high-viscosity pump and the gas supplied from the membrane gas generator. A pressurizing pump pressurizes the combination of the high-viscosity material and the gas discharged from the piston pump. A dispersing pipe passes the combination therethrough in a pressurized state to disperse the gas into the high-viscosity material to produce a mixture. A discharging device discharges mixture that has passed through the dispersing pipe.
The high-viscosity material can include an adhesive, a gap-filling sealing material, a coating material, a material for a foamed-in-place gasket, a material for a fill foam in a void, a damping material, a cushioning material, a lubricating grease and an insulating material. More specifically, the high-viscosity material may be a moisture curing material, a thermosetting material, a chemical reactive curing material or a hotmelt material. Of these, a material which hardens or solidifies immediately after foaming upon discharge is preferred in the method and apparatus of the present invention, from the viewpoint of achieving hardening or solidifying of the high-viscosity material with the gas being dispersed therein.
As the gas, a nitrogen gas, a carbon acid gas or air can be used. Instead of the membrane gas generator, a drier can be employed to pass air therethrough to generate such dry air. Such dry air can be used as the gas.
As the dispersing pipe for dispersing the gas in the high-viscosity material, for example, a hose or pipe having a length as large as from several to ten-odd meters is used. Such a hose or pipe may be straight or wound in an arc or a spiral. The hose or pipe may be used as a dispersing pipe unit mounted on and supported by a frame. By passing the combination of the high-viscosity material and the gas through the dispersing pipe in a pressurized state, the gas is formed into fine bubbles by shearing force and spread or dispersed in the high-viscosity material.
The membrane gas generator supplies a low-pressure gas having a pressure adjusted in a range of about 0.1 to 5 kg/cm2, preferably about 0.1 to 3 kg/cm2. The membrane gas generator separates gases in air by utilizing differences in membrane permeation velocity between the gases, thus generating a desired gas. The velocity at which a gas permeates a membrane depends on the solubility and diffusing ability of molecules of the gas with respect to the membrane. Nitrogen can be separated with high efficiency because, of the components of air, nitrogen has the lowest membrane permeation velocity. A nitrogen gas can be continuously obtained by supplying compressed air to the membrane gas generator.
Next, a mixing method of the present invention is. described with reference to the accompanying drawings.
Referring to FIG. 1, compressed air is supplied into a port 31. A gas is supplied under a pressure set by a pressure regulating valve 34 from a gas supplying device 10 to a pipe 39B. On the other hand, a motor M1A is controlled, and a high-viscosity material MV is supplied under a predetermined high pressure from a high-viscosity material supplying device 11 into a pipe 39A as desired, by means of a screw pump or a follower pump operated by rotating the motor M1A.
As shown in FIG. 4, a piston moves from a discharge end to a suction end of a cylinder, to thereby effect a suction stroke. During the suction stroke, when a time T1 has passed after start of the above movement of the piston, a needle valve NV1 opens, to thereby supply the gas into the cylinder. The needle valve NV1 closes after a short time after the piston has reached the suction end. Therefore, at the time of completion of the suction stroke, the cylinder is filled with the gas having the regulated pressure.
When a time T3 has passed after closing of the needle valve NV1, a needle valve NV3 opens. The needle valve NV3 is opened for a time period T4. During this period, the high-viscosity material MV is supplied from the high-viscosity material supplying device 11 into the cylinder. Due to high pressure of the high-viscosity material, the low-pressure gas, which has been supplied to the cylinder before supplying the high-viscosity material, is compressed in accordance with its pressure ratio relative to the high-viscosity material. Consequently, the volume of the gas in the cylinder becomes almost negligible.
For example, when the pressure of the gas is 1 kg/cm2 and the pressure of the high-viscosity material is 200 kg/cm2, the volume of the gas becomes about {fraction (1/200)}. In this case, the high-viscosity material in an amount equal to the volume of the cylinder is mixed with the gas of 1 kg/cm2 in the same volume. It should be noted that the gas of 1 kg/ cm2 in a volume equal to the volume of the cylinder is equivalent to the gas under atmospheric pressure (a pressure of 0 kg/cm2) in a volume twice that of the cylinder. That is, supplying the gas of 1 kg/cm2 into the cylinder is equivalent to pressurizing the cylinder to +1 kg/ cm2, as the pressure in the cylinder is a negative pressure of about xe2x88x921 kg /cm2 before supplying the gas during and/or after the suction stroke. Therefore, a mixing ratio R of the gas and the high-viscosity material when the volume of the gas is converted into that under atmospheric pressure is 2:1, since the gas is compressed by xc2xd relative to the volume of the cylinder. The mixing ratio R is expressed by a general formula Rxc2x1(P1+1):1 wherein P1 indicates the supply pressure of the gas. That is, the mixing ratio R can be easily adjusted or controlled by adjusting the supply pressure P1 of the gas.
When a time T5 has passed after closing of the needle valve NV3, a needle valve NV5 opens and the piston moves from the suction end to the discharge end, to thereby effect a discharge stroke. During the discharge stroke, the needle valves NV1 and NV3 are closed. When the needle valves NV1 and NV3 are closed, forward ends of the needle valves NV1 and NV3 are flush with an inner circumferential surface of the cylinder, so that a dead space within the cylinder becomes substantially zero and therefore, all the gas and the high-viscosity material in the cylinder are discharged from an opening of the needle valve NV5. When a time T6 has passed after completion of the discharge stroke, a subsequent suction stroke is started.
When a plurality of piston pumps are provided, the piston pumps are operated in a manner such that after the discharge stroke of one piston pump has been completed, the discharge stroke of another piston pump is started. Consequently, the high-viscosity material and compressed gas which are discharged in layers from each piston pump, are discharged continuously from the plurality of piston pumps into a pipe.